The invention relates to wireless ATM networks, and in particular to a remote or proxy signalling technique for the support of wireless and mobile broadband devices.
The invention has been developed in the context of a wireless broadband Asynchronous Transfer Mode (ATM) networking infrastructure which is capable of supporting multi-media data traffic at high bit rates in local and wide areas.
ATM is a packet switching and multiplexing technology using data packets of a fixed length called cells. It is designed to be a general purpose, connection-oriented, cell relay network supporting a wide range of guaranteed and best-effort Qualities of Service (QoS). ATM is a flexible and scalable technology which can operate at many bit rates over a number of physical media including Category 5 UTP and multimode fibre. The same protocols are used in both the local and wide-area enabling global end-to-end ATM interoperability.
Each cell has a short header containing a label, the Connection Identifier (CI), which identifies the payload as belonging to a particular connection or cell. This is composed of a Virtual Path Identifier (VPI) and a Virtual Circuit Identifier (VCI) and is used by each switching node to route the cell from the Input Port to the appropriate output port. The VPI:VCI is only a local identifier between two network elements and as such is changed as the cell traverses a switch.
In ATM networks, signalling is the means by which a connection is created (and deleted) between two endpoints, termed the Calling Party and the Called Party. Signalling takes place between network elements over a dedicated connection with a well-known VPI:VCI 0:5 as defined in the ATM Forum User-to-Network (UNI) and Network-to-Network (NNI) signalling standards.
These signalling protocols are defined in:
ATM User-Network Interface Specification, version
3.1, September 1994;
ATM User-Network Interface (UNI) Signalling Specification, Version 4.0, June 1996;
ATM Private Network-Network Interface Specification Version 1.0 (PNN1 1.0), March 1996; and
ITU-T Q.2931.
In conventional ATM signalling, signalling control messages proceed through the network in a hop-by-hop manner, following the same path as the connection which they reference. As such each network element is required to run full signalling stacks for each of its ports and provide full call control functionality.
Because signalling messages are important control messages used to maintain the connection state in the network, it is necessary to ensure their correct delivery between network nodes. In order to achieve this, signalling messages are carried over a reliable transport protocol called SSCOP. This protocol establishes connectivity between two signalling entities and ensures that messages are delivered reliably and in order between signalling peers.
Referring to FIGS. 1 and 2, in a wired ATM network, a first host 10, wishing to communicate with another host 12 sends a SETUP signalling message over its UNI on VPI:VCI 0:5 to the first network element in the connection path, the ingress switch 16. The switch 16 performs call admission control to decide whether the resources required for the requested connection can be allocated without violating the QoS guarantees of other connections traversing the switch. If the connection is accepted then that switch reserves resources for it and allocates a VPI:VCI for the hop to that switch. The SETUP is then routed to the next switch along the path over its NNI on VPI:VCI 0:5 where the same procedure is repeated. Thus each switch in the connection path carries out call admission control checks.
When the SETUP reaches the egress switch 18 on the path, it is forwarded to the called party 12 over its UNI 20 on VPI:VCI 0:5. The called party 12, if it chooses to accept the call, replies with a CONNECT signalling message. This message is routed back along the connection path, the connection being completed at each switch as the CONNECT message passes back to the calling party 10. Once the CONNECT message is received at the calling party 10 it is acknowledged and the connection is complete.
In the present invention, a remote, off-board agent, the xe2x80x98Proxy-Signalling Agentxe2x80x99 or PSA, which is usually a PC or a workstation, provides signalling and call control functionality for one or more of the network elements. In order to receive and transmit signalling messages on behalf of a network element, a bidirectional VC is provisioned, one for each port, from the network element to the PSA. For each network element under the control of the PSA, the PSA provides signalling stacks, one for each of the element""s ports, along with call admission control, routing and VCI allocation functions. This avoids the need for the network element to perform these functions.
The PSA controls the network element""s connection tables using a simple and low-level control protocol to effect changes in the connection state at that element, rather than using UNI. As the network element does not need to provide signalling stacks, it can be a low cost, low complexity device. By making these devices as simple as possible, we can increase the overall reliability of the network.
The invention is defined in more detail in the appended claims to which reference should now be made.